In electric shavers the shaving heads or cutter units get filled and polluted with the debris of shaving. Especially when a shaver is used with shaving cream or some other pre-shave additive applied to the face, this additive collects in the shaving heads or cutter units. Higher-end shavers often comprise a cleaning indicator. This is a symbol or user interface element that will activate, e.g. light up, to alert the user of the need to clean the shaver, in particular the shaving heads or cutter units.
The user interaction of known cleaning indicators in shavers is generally uniform, i.e. the cleaning indicator behaves in a similar way for all users and uses. Known cleaning indicators are generally activated based on time. They are for example activated after a predetermined number of minutes of shaving time or a predetermined number of shaving sessions. In some known shavers the cleaning indicator is even activated after every shaving session to prompt the user to clean.
With the above described known cleaning indicators, in the perception of the user the cleaning indicator provides a fairly arbitrary alert. This leads to an overall lower credibility of the shaver and less appreciation. When prompting the user to clean after every shaving session, the cleaning indicator is even unnecessarily burdening the user by negating the fact that the hair-chamber of the shaver is especially designed to accommodate the hairs and debris of several shaving sessions, and thereby loses credibility. When a user is prompted to clean after every shaving session, the user is burdened with the extra work of regular cleaning and does not experience a direct benefit from the presence of the cleaning indicator.
Patent publication U.S. Pat. No. 5,274,735 describes an electric shaver comprising a motor, a microcomputer and a current detecting circuit which detects the electrical current in the motor. The microcomputer is arranged to read, after the rotational speed of the motor has stabilized after start-up, a digital value outputted from an A/D converting circuit, and compare this value with a predetermined value set beforehand. When the detected motor current value is larger than the predetermined value, the microcomputer judges that an accumulated amount of shaving debris is increasing, and outputs a predetermined alert demanding cleaning of the shaver to a display of the shaver.
Nowadays, shavers are manufactured that may be used with different cutter units on a single main body. Storing a single predetermined value in such a shaver and comparing the actual motor current with the predetermined value, as is done by the shaver known from U.S. Pat. No. 5,274,735, may provide reliable cleaning alerting signals for just a single, individual cutter unit. But due to the power consumption variations between individual cutter units as well as the drift over time of the power consumption of an individual cutter unit, it will not be possible to provide reliable cleaning alerting signals using the technique used in the shaver known from U.S. Pat. No. 5,274,735.